The present invention relates to a ball ramp actuator which utilizes a ball ramp mechanism to apply a load or move another device, and more specifically, to a ball ramp actuator using a ball ramp mechanism to load or move another device where the relative rotation of the ball ramp mechanism is controlled through indexing plates to provide proper functioning regardless of the direction of torque flow through the ball ramp actuator.
The use of a ball ramp actuator to operate a driveline master clutch is known in the art. U.S. Pat. Nos. 5,441,137; 5,469,948; 5,505,285; 5,651,437; 5,810,141; 5,910,061; 5,964,330; and RE 36,502 assigned to the same assignee as this application, all of which are hereby expressly incorporated by reference, disclose methods of using a ball ramp actuator to supply the clamping force on a clutch disc and could, in the alterative, be used to supply a release force against a clutch apply spring.
Also shown in the prior art are other types of vehicle driveline devices which make use of a ball ramp mechanism to provide a clamping load on a clutch pack. U.S. Pat No. 5,092,825 discloses a limited slip differential having a clutch pack loaded by a ball ramp actuator. U.S. Pat. No. 5,499,951 discloses a driveline transfer case where the torque split is controlled by a ball ramp actuator. U.S. Pat. No. 5,528,950 discloses a transmission inertia brake where a ball ramp actuator loads a clutch pack to slow the rotation of a spinning transmission shaft. U.S. Pat. No. 5,819,883 discloses a driveline retarder in which a ball ramp actuator is used to load a clutch pack to rotate a hydraulic pump in response to a signal from a control unit. The disclosures of U.S. Pat. Nos. 5,092,825; 5,499,951; 5,528,950 and 5,819,883 are all hereby incorporated herein by reference.
The prior art ball ramp actuators used in the operation of a master clutch or other driveline coupling system such as a differential or transfer case could be improved by improving the inherent mechanical stability of the ball ramp. It would also be an advantage if the clutch remained fully engaged regardless of the direction of the flow of torque through the clutch when using a ball ramp mechanism with unidirectional grooves formed in the control and activation plates. Unidirectional grooves provide for increased separation distance capability since the axial depth variation in the grooves can be made greater because twice as much circumferential length is available as compared to a bi-directional groove.
Typically, a ball ramp mechanism is activated when an electrical current is supplied to a coil thereby producing an electromagnetic field in a coil pole which applies a retarding force to an armature which rotates with an input shaft. The rotating armature is nonrotatably connected to an annular control ring which has a plurality of control ramps or grooves formed in the face of control ring 20 which vary in axial depth. An annular activation ring which rotates with an output shaft has a like number of variable depth activation grooves formed therein which oppose those formed in the control ring where a corresponding number of rolling elements are trapped between the control and activation grooves. As a retarding force is applied to the control plate by the armature, the rotational movement of the control plate relative to the activation plate causes the rolling elements to simultaneously traverse the control grooves and the activation grooves thereby causing an increase in separation distance between the control and activation plates which is used to provide a clamping force on a clutch friction disc.
The present invention results in an improvement in the operational characteristics of a ball ramp actuator which can be used in a variety of vehicle driveline applications to provide a clamping load on a device such as a frictional clutch pack. The present invention provides for the same unidirectional apply ball ramp actuation function as disclosed in U.S. Ser. No. 09/940,821, assigned to the same assignee as this application, without using one-way clutches. Separate index plates are used to control the direction of rotation of both the control ring and the activation ring of the ball ramp mechanism, thereby functioning similar to the one-way clutches which they replace. In this manner, the reliability of the ball ramp mechanism is improved while manufacturing costs are reduced.
As taught in the U.S. Ser. No. 09/940,821 application, one-way clutches can be used to control the rotational direction of the control ring (plate) attached to the coil armature and the rotational direction of the activation ring (plate) to provide a continuous actuation function using unilateral grooves in the control ring and activation ring where the actuator force is maintained regardless of the direction of the flow of torque through the ball ramp mechanism. However, one-way clutches are expensive and not as reliable as the other components and the use of the index plates of the present invention in place of the one-way clutches results in a cost reduction with improved reliability.
The present invention provides the function of the one-way clutches using index plates which limit the degree of rotation of the control ring and the activation ring. The rotation limitation provided by the index plates is not exactly the same as provided with the one-way clutches, but for certain applications of a ball ramp mechanism, the functionality of the index plates is satisfactory. Specifically, a one-way clutch will lock-up during counter rotation after a relatively small degree of rotation on the order of one degree while the index plate of the present invention could allow as much as 240 degrees of rotation prior to lock-up. This 240 degrees of rotation is potentially operationally acceptable for use in many applications.
Thus, the present invention improves the performance and durability of a ball ramp actuator by eliminating the need for one-way clutches. Indexing plates are used to limit the relative rotational travel of the control ring and the actuation ring of the ball ramp mechanism which is used to apply an axial clamping load on a device such as a shift mechanism or a clutch pack. One indexing plate limits the rotation of the control ring of the ball ramp mechanism and a second indexing plate limits the rotation of the activation ring. Using the indexing plates of the present invention, the ball ramp mechanism, when energized, can only further move an actuator plate with relative rotation between the input and output shaft, thereby preventing any break in actuator torque. When the torque flows through, the ball ramp mechanism reverses direction. The indexing plates do not immediately prevent rotation in an undesired direction as with the one-way clutches disclosed in U.S. Ser. No. 09/940,821 but the ramp position and clamp load are locked in by the activation plate, intermediate plate and armature until the index plates hit against respective stops formed on the control ring and the activation ring. At that point the clamp load could be increased.
The present invention also results in an improvement in the operational characteristics of a ball ramp mechanism which can be used in a variety of vehicle driveline applications to supply a load to another device, such as a frictional clutch pack. The present invention provides a unidirectional apply ball ramp function which applies the actuator plate regardless of the direction of torque flow from the input to the output along with significantly increased frictional damping in the ball ramp mechanism itself due to the slipping of the activation plate, intermediate plate and armature (pilot section) during ramp movement to control and stabilize the ball ramp mechanism thereby improving the operation of the actuator.
To improve the operation of the ball ramp mechanism, the stability is improved by significantly increasing the frictional damping using an intermediate plate disposed between the activation plate and the control plate where the intermediate plate rotates with the output shaft and hub. The activation plate rotates with the activation ring joined with a slip sleeve and the control plate rotates with an armature. Note that the torque flow from the input shaft to the output hub can be reversed so that the torque flows from the output hub to the input shaft and the ball ramp actuator system will continue to provide the desired functionality.
To activate the ball ramp mechanism an electrical current is applied to a coil assembly which generates an electromagnetic force that frictionally rotationally couples a coil armature, a control ring, an intermediate plate and the activation ring together. With the rolling elements positioned at the bottom of the grooves the index plates are oriented to only allow the control ring to rotate in an opposite direction to that of the activation ring. An activation plate rotates with the activation ring supported on the input shaft while the intermediate plate is driven by the output hub while the coil armature rotates with the control ring which is rotationally supported on the input shaft. Thus, the activation plate or armature will slip as required to allow the control ring to rotate relative to the activation ring so as to further increase the clamping load generated by the ball ramp mechanism.
One provision of the present invention is to provide a ball ramp mechanism to load an actuator plate where the load is maintained regardless of the direction of the flow of torque through the actuator system.
Another provision of the present invention is to provide a ball ramp mechanism to load an actuator plate where the load is maintained regardless of the direction of the flow of torque through the actuator system using index plates with the ball ramp mechanism.
Another provision of the present invention is to provide a ball ramp mechanism to apply a load where the frictional damping of the ball ramp mechanism is substantially increased to improve operation.
Still another provision of the present invention is to provide a ball ramp mechanism to provide a load and/or motion having improved operational characteristics.